Device for Forming Conical Sections

ABSTRACT

A roll forming machine includes a frame supporting a conical drive roll rotatable on a fixed axis, and a conical pinch roll rotatable and movable transversely and angularly toward and away from the drive roll. Transversely movable and angularly adjustable forming rolls are disposed on opposite sides of the pinch and drive rolls, operable to selectively bend a workpiece frictionally held between the pinch and drive rolls and moved by their counter-rotation. The drive and pinch rolls rotate the workpiece about a transverse axis as they move the workpiece through the machine, enabling a consistent and accurate bending of workpieces to desired conical geometries. The machine can employ elongate drive and pinch rolls with guides to selectively place the workpieces along the rolls, to controllably vary the ratio of small-end to large-end radii in shaped pieces. Alternative versions feature a single forming roll, and rolls that alternatively serve the pinching and forming functions.

BACKGROUND OF THE INVENTION

The present invention relates to roll forming machines for imparting controlled curvature to relatively thick plates or sheets of malleable metal, and more particularly to apparatus and methods for forming flat panels into frusto-conical shapes.

Roll forming machines have been used for many years to controllably curve sheet metal stock. For example, cylindrical pipe sections are formed by feeding initially planar rectangular panels of malleable steel between a pair of rotating rolls, with another roll spaced apart transversely to impart a bending force corresponding to a desired pipe diameter.

In one type of machine, known as a pyramid roll forming machine, a pair of lower, in-line rolls support a sheet or panel for horizontal travel as it is being contoured by an upper, transversely adjustable roll located midway between the lower rolls. Because bending occurs only under the upper roll, the leading and trailing edges of the panel are not subject to bending by the rolls. Consequently they are either preformed, or shaped after forming the majority of the pipe section.

This problem can be counteracted in a design known as the initial pinch roll machine. In this approach, the top roll is offset to be on top of one of the bottom rolls, which functions as a pinch roll while the other lower roll functions as the bending roll. This allows controlled curvature of the leading edge, and enables the trailing edge to be curved as well by removing the panel and reloading, trailing edge first.

According to a further improvement, the rolls are adjustable transversely to allow each of the lower rolls to function, alternatively, as the pinch roll and as the bending roll.

Yet another roll forming device includes four rolls: a pair of pinch rolls that can be spaced apart vertically, and two bending or forming rolls spaced apart horizontally from the pinch rolls, one on each side. As a panel or sheet is fed into the space between the pinch rolls and initially clamped, the trailing or upstream forming roll is transversely moved to apply the desired bending force. At some point before the trailing edge of the panel clears the upstream forming roll, the leading or downstream forming roll is moved transversely into contact with an already curved portion of the panel, and thus is positioned to function as the forming roll to apply the desired curvature to the trailing edge of the panel.

Although roll forming machines are used primarily to shape uniformly thick flat panels into constant diameter tubular shapes, designers have attempted to increase the versatility of these machines. For example, U.S. Pat. No. 4,117,702 (Foster) discloses pinch and pyramid roll forming machines for contouring structural members that are tapered, with varying thicknesses. To this end, each of the pinch rolls and forming rolls is formed with two segments, one of which floats transversely relative to the other to accommodate a variable thickness.

Another, more common modification is a snubber or stop used in conjunction with the pinch rolls to form flat panels into frusto-conical shapes. Typically, the snubber is aligned to engage the leading edge of the panel at or proximate a selected one of the panel side edges. Although engagement with the snubber prevents further forward movement at the selected side edge, the pinch rolls continue to act upon the panel, causing the panel to rotate about an axis perpendicular to the major plane of the panel, i.e. in the panel thickness direction. The rotation, in combination with a transverse bending force applied through a forming roll, imparts a conical shape.

Although this approach is satisfactory for limited applications, it is subject to difficulties. One of these is an unavoidable skidding of the panel as it rotates while the pinch rolls attempt to drive it forward. This skidding leads to momentary slippage of the panel relative to the pinch rolls. As a result, the panel does not rotate smoothly and precisely about the given axis. Instead, the panel moves through a series of minute twists in which the leading edge near the selected side edge is momentarily retracted from the snubber, then quickly brought back into engagement with the snubber by the forward motion of the pinch rolls. The result is a slight but undesirable twist in the finished conical piece.

The twisting tendency can be counteracted to a degree by altering the distance between the pinch rolls. This, however, leads to a frusto-conical piece with a larger than desired diameter at its smaller end, necessitating further adjustments including changes in the angles of the forming rolls.

Determining the appropriate adjustments and the degree of each adjustment to achieve satisfactory results, requires considerable experience and skill on the part of the machine operator. Even then, precise frusto-conical geometries are difficult to achieve in view of the unavoidable slippage and skidding of the panels.

The ability to form flat panels into precise truncated conical shapes could improve a wide variety of manufacturing processes. Of particular interest are processes for fabricating revolving drums for concrete transit mixers. The mixing drums have truncated conical sections. Each section consists of several curved panels welded together to form the required 360 degree arc; e.g. four panels each encompassing an arc of 90 degrees. Due to the strength and durability required of the mixing drum, the panels are relatively thick, e.g. 3/16 to ¼ inches. The capability to form the panels according to precise conical geometries would considerably enhance the mixing drum manufacturing process, eliminating the need to elastically bend panels into the desired curvature for welding. In addition, accurately curved panels would be easier to position and align prior to welding. Conventional roll forming processes, however, fail to provide this capability.

Accordingly, the present invention has several aspects, each directed to one or more of the following objects:

-   -   to provide a device for accurately and repeatedly forming flat         panels into selected frusto-conical geometries according to         predetermined ratios of opposite end radii;     -   to provide a process for forming flat panels or sheets into         curved segments tapered according to a selected ratio of         opposite end radii and adjustable over a range of small end         radii and large end radii that satisfy the selected ratio;     -   to provide roll forming machinery capable of selectively curving         flat panels over a range of opposite end radii ratios and         adjustable to select a particular value for the ratio within the         range; and     -   to provide a process for manufacturing drums for concrete         transit mixers in which the panels used to form frusto-conical         sections of the drum are precisely shaped before they are welded         together.

SUMMARY OF THE INVENTION

To achieve the forgoing and other objects, there is provided a roll forming machine. The machine includes an elongate first roll having a first roll axis. The first roll is substantially uniformly tapered over a first region extending axially between a first axial location having a first diameter and a second axial location having a second diameter larger than the first diameter. The machine includes an elongate second roll having a second roll axis. The second roll is substantially uniformly tapered over a second region extending axially between a third axial location having a third diameter and a fourth axial location having a fourth diameter larger than the third diameter. The machine further includes an elongate third roll rotatable on a third roll axis. A roll mounting structure is coupled to the first and second rolls to support the first and second rolls in side-by-side relation for rotation about the first and second roll axes, respectively. So supported, the first axial location is proximate the third axial location and the second axial location is proximate the fourth location. The first and second rolls are inclined relative to one another whereby the first and second roll axes intersect. First and second confronting surfaces of the first and second regions extend longitudinally, separated by a substantially constant transverse spacing to facilitate a frictional hold of a uniformly thick workpiece between the first and second regions with a major plane of the workpiece perpendicular to an alignment plane containing the first and second roll axes. The roll mounting structure is operable to counter-rotate the first and second rolls about the first and second axes respectively during said frictional hold, thereby to effect a rotation of the workpiece about a transverse rotational axis lying in the alignment plane. The roll mounting structure further is coupled to support the third roll in side-by-side, transversely spaced apart relation to the first and second rolls, and is operable to selectively move the third roll transversely relative to the first and second rolls to apply a predetermined bending force to the workpiece during said hold and rotation.

Preferred versions of the machine include a fourth roll rotatable on a fourth roll axis. In these versions, the roll mounting structure supports the fourth roll in side-by-side, transversely spaced apart relation to the first and second rolls on an opposite side of the alignment plane from the third roll. The fourth roll, like the third roll, is selectively movable transversely relative to the first and second rolls to apply the predetermined bending force to the workpiece as it is held between and rotated by the first and second rolls. In this arrangement, the desired conical geometry can be imparted to the panel in a single pass through the machine, with no need to preform either the leading edge or the trailing edge.

The first and second rolls preferably are frusto-conical, with outer surfaces inclined from their respective roll axes by an angle in the range of 1-3 degrees, resulting in opposite side edges of the rollers inclined relative to one another by an angle in the range of 2-6 degrees.

In spite of the relatively narrow range, the machine can be used to shape panels into conical sections with considerably larger angles of incline between the outer surface of a given section and its central axis. This is because the incline is determined in large part by the degree of bending, along with the ratio of the roll diameters at the opposite side edges of the panel. In general, given a constant ratio of diameters, enlarging the diameters themselves leads to a steeper angle of inclination.

The third roll, as well as the fourth roll in versions with four rolls, preferably has a constant diameter over its entire length. Although the third and fourth rolls could be tapered and inclined to match the first and second rollers if desired, the aforementioned skidding and slippage problem has a minimal impact on the third and fourth rolls, due to the much lower pressure against the panel associated with bending as opposed to pinching. Further, providing bending rollers that are straight rather than tapered leads to a more versatile machine.

Another aspect of the invention is an apparatus for shaping substantially planar sheet metal panels into truncated conical wall sections for a drum. The apparatus includes a first elongate truncated conical roll having a first roll axis. The apparatus includes a second elongate truncated conical roll having a second roll axis. A roll mounting structure is coupled to the first and second rolls to support the first and second rolls in side-to-side relation, tapered in the same direction. The rolls are inclined such that the first and second roll axes intersect. Confronting first and second surface portions of the first and second rolls, respectively, extend longitudinally and are separated from one another by a substantially uniform transverse spacing. A power component is provided for counter-rotating the first and second rolls with a substantially planar formable sheet metal panel frictionally held by a thickness thereof between the first and second confronting surface portions, to rotate the panel about a transverse rotational axis lying in an alignment plane defined by the first and second roll axes. A panel bending component is operable to apply a controlled bending force to the panel substantially in the direction of said thickness while the panel is so held and so rotated.

Preferably, the apparatus includes a stop positioned to abut a leading edge of the panel as the panel is inserted transversely between the first and second rolls, to prevent further transverse movement of the panel beyond a predetermined initial position for holding between the rolls. The apparatus also can include a guide member positioned to contact a side edge of the panel as the panel is inserted between the rolls, thus to determine a longitudinal location of the panel with respect to the first and second rolls. The stop and guide member preferably are configured for retraction away from the first and second rolls in response to movement of the first and second rolls together to grip the panel.

In highly preferred versions of the apparatus, two or more guide members can be positioned to determine several different placements of the panel longitudinally with respect to the first and second rolls. For a panel of a given width, the different longitudinal placements result in different ratios between the larger and smaller diameters of the finished conical sections. Accordingly, the apparatus is considerably more flexible in terms of the sizes and inclinations of the frusto-conical sections that may be fabricated.

The preferred bending component is an elongate third roll supported in side-by-side transversely spaced apart relation to the first and second rolls. The roll is movable transversely relative to the first and second rolls to apply the desired bending force. Preferred versions of the apparatus further include a fourth roll, supported and operated in the same manner as the third roll, on the opposite side of the first and second rolls.

A further aspect of the present invention is a process for forming planar malleable panels according to conical geometries; including the following steps:

a. providing a conical drive roll and a conical pinch roll rotatable about respective drive roll and pinch roll axes and inclined relative to each other whereby said axes intersect to define an alignment plane, with first and second confronting surfaces of the drive and pinch rolls, respectively, extending longitudinally and separated from one another by a substantially uniform transverse spacing;

b. providing a substantially planar and uniformly thick panel formed of a malleable material with oppositely inclined leading and trailing edges, substantially parallel side edges, and a leading edge region adjacent to and incorporating the leading edge;

c. positioning the panel with the leading edge region disposed between the first and second confronting surfaces, with a major plane of the panel perpendicular to the alignment plane, and with the leading edge extending longitudinally;

d. with the panel so positioned, transversely moving at least one of the drive roll and the pinch roll to reduce the transverse spacing to effect a frictional hold of the panel between the drive roll and the pinch roll;

e. during the frictional hold, counter-rotating the drive roll and the pinch roll to rotate the panel about a transverse rotational axis perpendicular to the alignment plane; and

f. while so rotating the panel, applying a controlled bending force to the panel in a direction substantially perpendicular to the major plane.

A preferred approach to effecting the frictional hold of the panel is to maintain the drive roll axis fixed while moving the pinch roll toward the drive roll. Counter-rotating the drive roll and pinch roll is advantageously accomplished by coupling a motive power source to the drive roll only. The pinch roll rotates with the drive roll, by virtue of its frictional coupling to the drive roll through the captured panel.

In one particularly preferred approach, steps b-f recited above are preformed several times to provide several frusto-conically shaped panels. Each panel is shaped to have arcuate first and second opposite side edges encompassing an arc of less than 360 degrees, with the second edge having a radius larger than the radius of the first edge. For example, four panels can be shaped, each encompassing a 90 degree arc.

Next, the panels are assembled end to end with the leading and trailing edges of adjacent panels contiguous, to form a continuous frusto-conical wall section encompassing 360 degrees. With the panels thus assembled, the contiguous leading and trailing edges are bonded to form the panels into an integral frusto-conical wall section.

A salient feature of the present invention presides in the use of selectively tapered pinch and drive rolls to rotate the panel in a controlled manner while applying a controlled bending force to the panel. The skidding and slippage problems associated with conventional roll forming machinery are eliminated, leading to a more precise and more repeatable shaping of multiple panels into a predetermined conical geometry. Another feature resides in providing pinch and drive rolls considerably longer than the widths of the panels being shaped, e.g. at least twice the width. This permits different selected longitudinal alignments of panels along the rolls, to achieve different ratios of the radii at opposite ends of the finished conical shape. The ability to selectively and accurately shape frusto-conical sections enables and facilitates fabrication of mixing drums for concrete transit mixers and other structures that incorporate frusto-conical sections.

IN THE DRAWINGS

For a further understanding of various features and advantages of the present invention, reference is made to the following detailed description and to the drawings, in which:

FIG. 1 is a frontal elevation of a tapered roll plate bending machine constructed in accordance with the present invention;

FIG. 2 is a side elevation of the machine;

FIG. 3 is a top plan view of the machine showing the rolls of the machine in phantom;

FIG. 4 is a schematic top view illustrating roll position and range of adjustment;

FIG. 5 is a schematic side view of the drive roll and pinch roll;

FIG. 6 is a schematic frontal view illustrating the pinch roll;

FIGS. 7 a-c are schematic top views illustrating a plate bending sequence;

FIG. 8 is a prospective view of a plate bent into a frusto-conical shape;

FIG. 9 is a prospective view illustrating a plurality of frusto-conical shaped plates arranged for welding into a frusto-conical section of a mixing drum;

FIG. 10 is a side elevation of a concrete transit mixing vehicle;

FIG. 11 is a schematic top view illustrating the rolls of an alternative version plate bending machine;

FIG. 12 is a schematic view similar to that of FIG. 11 following a roll position adjustment;

FIG. 13 is a schematic top view of the rolls of another alternative plate bending machine; and

FIG. 14 is a schematic view similar to that of FIG. 13 following a roll position adjustment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIGS. 1-3 a tapered roll plate bending machine 16. The machine has a structural frame 18 consisting of several sections welded together into an integral unit. These include an upright main frame section 20, a top frame section or housing 22, and a bottom frame section or housing 24.

A plurality of rolls extend lengthwise between housings 22 and 24, mounted for rotation with respect to frame 18 about vertical or nearly vertical axes. These include a drive roll 26, a pinch roll 28, and first and second forming or bending rolls 30 and 32. Opposite ends of each roll are mounted to the frame through roller bearing cases inside the top and bottom housings. A hydraulic motor is employed to rotate drive roll 26, about an axis fixed with respect to the frame. Hydraulic cylinders are used to controllably move rolls 28, 30, and 32 in transverse directions relative to frame 18.

The bearing casings and hydraulic cylinders are not shown or described in detail, as these components and their use in plate bending machines is familiar to those of skill in the art. In addition, it is to be appreciated that the vertical orientation of the rolls is not critical, as they can be configured to rotate on substantially horizontal axes.

Drive roll 26 and pinch roll 28 are tapered, each diverging in the downward direction from a smaller diameter near the top of the roll to a larger diameter near the bottom. In one version of machine 16, drive roll 26 and pinch roll 28 have a working length of six feet, a top diameter of eight inches and a bottom diameter of twelve inches. In another version, the length and bottom diameter are the same while the top diameter is 5.5 inches. In each of these versions, the angle between opposite sides of the tapered rolls as viewed in a plane including the roll axis is small, about three degrees and about five degrees respectively. More generally, the angle between the inclined surface of the roll and the roll axis may be five degrees or less. Thus, the rolls appear cylindrical.

Forming rolls 30 and 32 are substantially cylindrical in shape. More precisely, they are crowned, i.e. configured with a diameter that increases slightly in the directions from the opposite ends toward the medial region of the roll. Crowning compensates for the tendency of the rolls to bend in response to transverse pressure during normal forming operations. The required crowning is slight, e.g. several one-hundredths of an inch for a six foot long roll having a nominal diameter of twelve inches. The required crowning varies, calculated or predetermined in each case depending mainly on the required bending forces.

Like the forming rolls, drive roll 26 and pinch roll 28 are crowned to compensate for the tendency of the rolls to bend during forming operations. Due to the taper of these rolls, crowning is not symmetrical about the medial region of the roll, but is more pronounced along the narrower region of the roll to compensate for an increased bending tendency. Nonetheless, the degree of diameter variance due to crowning remains slight, on the order of several one-hundredths of an inch.

In machine 16 the pinch and forming rolls function as idlers, rotated by friction when engaged with a workpiece being moved through the machine by powering the drive roll. In alternative versions of the machine, one or more of the other rolls, typically the pinch roll, can be powered in concert with the drive roll. In these versions, however, the lack of precise synchronization of the powered rolls can result in an inaccurately dimensioned workpiece. As illustrated in FIG. 3, pinch roll 28 further is movable transversely and linearly over a limited range to selectively adjust a transverse or horizontal spacing between the drive and pinch rolls. The range of motion, typically only several inches, is exaggerated in the figure to emphasize this feature. Bearing cases at the top and bottom ends of pinch roll 28 are independently moveable to determine the orientation of the roll relative to the frame.

With further reference to FIG. 3, forming rolls 30 and 32 are supported for limited arcuate travel, between respective advanced positions 30 a and 32 a for bending a workpiece held between the pinch and drive rolls, and retracted positions 30 b and 32 b for loading a workpiece to be formed, and removing the formed workpiece. The forming rolls, like the pinch roll, are adjusted through controlled movement of opposite-end bearing cases. The bearing cases associated with each forming roll are movable independently of one another to selectively change the forming roll orientation, i.e. the angle of each forming-roll axis relative to the frame. The range of bearing case motion is limited such that the forming-roll axes remain substantially vertical. In alternative machines, rolls 30 and 32 can be supported for travel along substantially linear or radial paths.

Also illustrated in FIG. 3 is a workpiece guide 34, reciprocable between an advanced position 34 a and a retracted position 34 b. When advanced, guide 34 is positioned for engagement with a workpiece leading edge region to accurately position and orient the workpiece with the leading edge region disposed between drive roll 26 and pinch roll 28. The guide is retracted after the pinch roll has moved toward the drive roll to capture and frictionally hold the workpiece.

A control console 36 is operatively coupled to the hydraulic cylinders that move the rolls, to control the rotational speed of drive roll 26, the location of pinch roll 28, the locations of forming rolls 30 and 32 along their respective arcuate paths, and the orientation of the forming rolls. The console is advantageously physically separated from frame 18 as shown, and can incorporate manual control features such as buttons, dials and foot pedals, along with computer-responsive features that allow the operator to program drive roll nominal rotational speed and direction, forces applied to a workpiece between the drive roll and the pinch roll, and the degree of bending as determined by the extent to which either forming roll is advanced.

In an alternative version of the plate bending machine, a separate hydraulic motor is employed to rotate the pinch roll about the pinch roll axis. The control panel, operatively coupled to the motors that rotate the drive and pinch rolls, synchronizes the motors to rotate the drive and pinch rolls in opposite directions at the same angular speed. Where needed or desired, this arrangement improves traction on the workpiece to more effectively avoid slippage. In further alternative embodiments, hydraulic motors can be used to rotate the forming rolls at speeds synchronized with the drive and pinch rolls. This approach, as noted earlier, requires highly accurate synchronization.

FIG. 4 is a schematic top view of drive roll 26, pinch roll 28, and forming rolls 30 and 32, positioned to receive a flat plate or workpiece 38 to be bent into a predetermined conical shape. The workpiece has a substantially uniform thickness. A leading edge 40 of workpiece 38 is positioned between drive roll 26 and pinch roll 28, engaged with leading edge contact features 42 of guide 34 to align the workpiece with the drive and pinch rolls. To facilitate workpiece loading, forming roll 32 is retracted and the drive and pinch rolls are separated by a transverse distance that exceeds the workpiece thickness. The circular top edges of drive roll 26 and pinch roll 28 do not appear concentric with the bottom edges of these rolls, although in practice the top and bottom edges are concentric. This is because rolls 26 and 28 are tilted with respect to the vertical, to align their confronting or opposing surfaces.

This is seen more clearly in FIG. 5, a side elevation of rolls 26 and 28 as supported by frame 18. A longitudinal axis 44 of machine 16 is vertical. A drive-roll axis 46 and a pinch roll axis 48 are inclined from the vertical axis in opposite directions, by the same angle. An outer surface 50 of drive roll 26 is inclined relative to drive-roll axis 46 at the same angle that the drive-roll axis is inclined to vertical axis 44. Likewise, an outer surface 52 of pinch roll 28 is inclined from the pinch-roll axis at the same angle. As a result, confronting surfaces 54 and 56 of rolls 26 and 28, i.e. the sections of their outer surfaces that directly face or confront one another at any given time, are vertical, spaced apart from one another by a transverse (horizontal) distance that remains substantially uniform over the length of the rolls.

With further reference to FIG. 5 and FIG. 6, guide 34 includes a side edge contact feature 58 positioned to support workpiece 38 at the bottom of the leading edge region, to align the workpiece axially relative to the drive and pinch rolls. In particular, a top edge of the workpiece is aligned with an upper axial location 60 of drive roll 26, and a bottom edge of the workpiece is aligned with a lower axial location 62 of the drive roll. Likewise, the top and bottom edges are aligned with upper and lower axial locations 64 and 66 along pinch roll 28. At upper locations 60 and 64, rolls 26 and 28 have a diameter D₁. At lower locations 62 and 66, these rolls have a diameter D₂ larger than diameter D₁. As pinch roll 28 is moved transversely toward drive roll 26, the workpiece leading edge region near leading edge 40 becomes captured between the drive and pinch rolls, frictionally held due to pressure applied through confronting surfaces 54 and 56.

Axes 46 and 48 intersect vertical axis 44 and each other at a common point 68 above rolls 26 and 28. These axes cooperate to define a plane incorporating them, conveniently considered as an alignment plane of machine 16. When workpiece 38 is loaded into the machine and frictionally held between rolls 26 and 28, its major plane, i.e. the plane perpendicular to the thickness and defined by the length and width dimensions, is perpendicular to the alignment plane. Common point 68 also locates a workpiece rotational axis 70, a transverse axis located in the alignment plane. When drive and pinch rolls 26 and 28 are counter-rotated to carry workpiece 38 through the machine, they rotate the workpiece about rotational axis 70.

The taper of rolls 26 and 28, and the inclination of axes 46 and 48 from the vertical, are exaggerated in FIG. 5 to facilitate an understanding of the principles involved. In practice, the angles of incline are in the range of 1.5 to 2.5 degrees.

A given incline or taper of the drive roll and pinch roll, e.g. 2 degrees, does not result in the same taper in a formed conical workpiece. Rather, the finished workpiece shape is determined primarily by two factors: (1) the amount of bending, as determined by how far the forming rolls are advanced; and (2) the ratio of the top edge diameter to the bottom edge diameter in the finished piece. With reference to FIG. 5, this ratio can be expressed as a ratio of the distance between common point 68 and upper axial location 60, to the distance between common point 68 and lower axial location 62. When workpiece 38 is correctly axially aligned with respect to rolls 26 and 28 as shown in FIGS. 5 and 6, upper side edge 74 coincides with axial locations 60 and 64, and workpiece lower side edge 72 coincides with axial locations 62 and 66.

The workpiece is axially aligned with reference to the roll geometry, in that the length ratio of side edge 74 to side edge 72 (i.e. the expected ratio of the top edge diameter to the bottom edge diameter in the finished piece) is equal to the roll diameter ratio D₁/D₂ based on diameters D₁ and D₂ taken at locations 60 and 62, or at locations 64 and 66.

Correct axial alignment is a key factor in shaping the workpiece as desired. If workpiece 38 were placed closer to common point 68, i.e. moved upwardly as viewed in FIGS. 5 and 6, side edges 72 and 74 would coincide with different axial locations along rolls 26 and 28. As compared to the correct axial locations, the new axial locations would be higher and have smaller the diameters. More importantly, the ratio of the smaller (higher) diameter to the larger (lower) diameter would be less than desired. As a result, the finished piece would be more conical, or more steeply inclined, than desired. Conversely, lowering workpiece 38 relative to the position illustrated would align side edges 74 and 72 with larger diameter locations along rolls 26 and 28. The roll diameter ratio (smaller diameter to larger diameter) would be higher than desired, resulting in a finished workpiece more cylindrical (more gradually inclined) than desired.

FIG. 6 is a schematic frontal view illustrating the position of workpiece 38 with respect to pinch roll 28. Drive roll 26, not shown, would be in front of the pinch roll in this view.

Workpiece 38 is a flat plate in which side edge 72 is longer than opposite side edge 74 and extends outwardly beyond side edge 74 by equal amounts on both sides of the plate. Accordingly, leading edge 40 and trailing edge 76 are inclined oppositely at the same angle. Guide 34, with contact feature 42 engaging leading edge 40 and contact feature 58 engaging side edge 72, aligns workpiece 38 as shown.

A broken line 78 extending from leading edge 40, and a broken line 80 extending from trailing edge 76, intersect at rotational axis 70, which appears as a point in FIG. 6. Edges 40 and 76 are linear. Side edges 72 and 74 are arcuate and parallel, both curved about axis 70 when workpiece 38 is positioned as shown. The curvature of side edges 72 and 74 is gradual, giving workpiece 38 a generally trapezoidal shape.

A sequence of operation for bending workpiece 38 into a desired conical shape is now described with reference to FIGS. 7 a-c. With the workpiece initially positioned as shown in FIGS. 4-6, pinch roll 28 is advanced toward drive roll 26 to capture the leading edge region of the workpiece between these rolls. After initial pinch roll advancement, workpiece guide 34 (not shown here) is retracted to remove it from the path traversed by the workpiece during shaping. With the workpiece firmly held between rolls 26 and 28, forming roll 32 is advanced by a predetermined amount based on the desired amount of bending. This result is shown in FIG. 7 a.

Advancing forming roll 32, and similarly advancing forming roll 30, involves predetermining the roll orientation as well as the extent of advancement. The correct angle of the forming-roll axis depends on a variety of factors including primarily the thickness of the workpiece, the upper-edge and lower-edge diameters of the finished piece, and the bending properties of the workpiece material. One or more test runs may be required to determine the correct angle. For example, if a test run yields a finished piece with the correct bottom edge diameter and a top edge diameter that is too large, the top-end bearing cases of the forming rolls are advanced to tilt their axes in a counterclockwise direction as viewed in FIGS. 2 and 5. Forming rolls 30 and 32, spaced equally from rolls 26 and 28 on opposite sides, are adjusted to the same degree of advancement and orientation.

After correctly advancing and orienting forming roll 32 to form the initial bend, drive roll 26 is rotated counterclockwise as viewed in FIGS. 4 and 7 a to move the workpiece to the left. This also rotates the workpiece about workpiece rotational axis 70, due to the progressive increase in linear roll velocity in the downward direction occasioned by the gradual increase in roll diameter in that direction, coupled with a constant angular velocity. This initial translation of the workpiece through machine 16 is shown in FIG. 7 b. Thus, the workpiece is continually formed along portions located between the drive and pinch rolls as the workpiece is carried past the rolls.

In machine 16, pinch roll 28 is rotated at the same angular rate as drive roll 26, by virtue of its frictional engagement with the drive roll through their mutual contact with the workpiece. In alternative versions of the machine, the drive roll and pinch roll are separately driven for improved traction on the workpiece to help prevent slippage. Their rotational speeds must be precisely synchronized to achieve the necessary matching of progressive linear speeds.

At some point during movement of workpiece 38 through the machine, forming roll 30 is advanced and oriented to bend the workpiece. This is accompanied by retraction of forming roll 32, shortly before advancement of forming roll 30. At this stage, roll 30 rather than roll 32 functions as the forming roll, although there may be a brief transition during which neither of these rolls engages the workpiece. The transition from roll 32 to roll 30 preferably occurs early in the workpiece translation cycle, e.g. following about eight to twelve inches of workpiece travel past rolls 26 and 28. The transition in any event must occur before trailing edge 76 of the workpiece reaches roll 32.

Following the transition, counter-rotation of rolls 26 and 28 continues until a trailing edge region of the workpiece is captured between these rolls, as shown in FIG. 7 c.

As noted previously, the shape of the formed workpiece is determined primarily by the advancement of the forming rolls (augmented by their orientation or angle), and the ratio of the expected diameters at the workpiece top edge and bottom edges after the workpiece is bent. The initial shape of workpiece 38 is predetermined with regard to the expected shape of the finished workpiece, in that the length ratio of side edge 74 to side edge 72 matches the expected ratio of the top edge diameter to the bottom edge diameter in the finished piece. This in turn matches the roll diameter ratio D₁/D₂ corresponding to axial locations 60 and 62 along roll 26 (and to locations 64 and 66 along roll 28) that coincide with the top and bottom edges of the properly aligned workpiece. Again, it is noted that the roll diameter ratio D₁/D₂ is specifically tied to the designated axial locations, i.e. 61 and 62 or 64 and 66. If the workpiece is misaligned such that the side edges do not coincide with these axial locations, the diameter ratio is either too small, resulting in a part that is more conical than desired, or too large, resulting in a finished part more cylindrical than desired.

FIG. 8 is a perspective view of workpiece 38 after it has been shaped into the desired conical configuration to form a frusto-conical wall piece 82. The terms “conical” and “frusto-conical” are used broadly, to apply not only to complete (360 degree) sections, but also to arcuate pieces or sections. For example, in wall piece 82 edges 72 and 74, and the wall piece as a whole, encompass an arc of ninety degrees.

The fabrication of a truncated-conical wall section involves forming four generally trapezoidal plates according to the sequence just described, to provide four frusto-conical wall pieces. As seen in FIG. 9, wall pieces 82, 84, 86, and 88 are supported by a framework 90, end to end, to form a continuous frusto-conical wall section 92 encompassing 360 degrees. Two seams are visible: a seam 94 between a leading edge 96 of piece 82 and a trailing edge 98 of piece 84, and a seam 100 between a leading edge 102 of piece 84 and a trailing 104 edge of piece 86. The remaining two seams are disposed behind framework 90.

With the wall pieces held against framework 90 by clamps or fixtures (not illustrated), the seams are welded to provide finished frusto-conical wall section 92.

The forgoing process is particularly useful for fabricating containers with frusto-conical wall sections, because of the capacity to consistently shape the wall sections and their component pieces with accuracy. One prominent container of this type is a revolving mixing drum for a concrete transit mixer.

FIG. 10 is a diagrammatic side view of a concrete transit mixing vehicle 106 with a cab 108, a chassis 110, and wheels 112 supporting the cab and chassis. A mixing drum 114 is supported for rotation relative to the chassis about an axis inclined upwardly to the right as viewed in the figure. Near the rearward end of the drum are a hopper 116 for loading water, cement and aggregate into drum 114, and a discharge chute 118 used to direct the mixed concrete to a desired location.

Mixing drum 114 includes a frontal section or head 120, a cylindrical medial section or belly 122, a frontal conical section 124, a rearward conical section 126 directly behind the belly, and a slightly more steeply inclined rearward conical section 128 behind section 126. Conical sections 124, 126, and 128 have different inclines in the axial direction, and different ratios of small-end radius to large-end radius.

A salient feature of machine 16 is the flexibility afforded by making drive roll 26 and pinch roll 28 much longer than required to form any one of mixing drum sections 124, 126, and 128. As noted above, side edge contact feature 58 axially aligns the workpiece. This determines locations 60/64 and 62/66 along the rolls, thus to determine roll diameters D₁ and D₂ and the ratio D₁/D₂. The longer rolls allow alternative axial positioning of the workpiece to select different axial locations along the rolls to coincide with the workpiece upper and lower edges. This raises or lowers the roll diameter ratio, resulting in a finished piece more conical or more cylindrical, as desired.

With general reference to FIG. 10, assume that conical sections 124 and 126 are to be formed from generally trapezoidal plates with a width or height of three feet. Further, assume that conical section 124 is steeper than section 126; i.e. the design ratio of small-end diameter to large-end diameter is smaller for conical section 124. Finally, assume that pinch roll 28 and drive roll 26 are six feet long with an upper-end diameter of eight inches and a lower-end diameter of twelve inches.

The desired shaping is achieved by using two guides similar to guide 34, each with its own leading edge contact features and side edge contact feature. The first guide, near the longitudinal midpoints of rolls 26 and 28, longitudinally aligns the workpiece with the upper halves of the rolls to form pieces for section 124. Accordingly, the upper-end diameter to lower-end diameter ratio is 8/10 or 0.800. To form pieces for section 126, the workpiece is aligned with the lower halves of rolls 26 and 28. The resulting diameter ratio is 10/12, or 0.833.

The diameters of the finished wall pieces forming sections 124 and 126 are determined in large part by the degree of bending. For example, assuming that belly 122 has a diameter of six feet, the large-end diameters of sections 124 and 126 likewise are six feet. The small-end diameters of sections 124 and 126 are 4.8 feet and 5 feet, respectively.

The range of diameter ratios, 0.800 to 0.833, is well suited for fabricating mixing drum 114 and similar containers. In applications that call for a wider range of diameter ratios, the length of the drive and pinch rolls can be increased as compared to the widths of the workpieces involved. More steeply inclined drive and pinch rolls yield more steeply inclined wall pieces and wall sections, and further expand the range of diameter ratios.

FIGS. 11 and 12 schematically illustrate the three rolls of an alternative embodiment machine of the “pinch pyramid” type. A drive roll 130 is hydraulically powered to rotate relative to a machine frame (not shown) about a drive-roll axis that is fixed with respect to the frame. Rolls 132 and 134 are rotatable about respective roll axes, and are movable transversely relative to the drive roll along either arcuate or linear paths. Each of rolls 132 and 134 is configured to function alternatively as a pinch roll and as a forming roll. In FIG. 11, roll 132 acts as a pinch roll to grip a workpiece 136 in cooperation with drive roll 130, while roll 134 functions as the forming roll. Drive roll 130 is rotated in a clockwise direction, to move the workpiece from right to left as viewed in the figure.

Before the trailing edge of workpiece 136 reaches roll 134, the roll positions are reversed so that roll 134 cooperates with the drive roll to grip the workpiece as viewed in FIG. 12. Roll 132 is positioned and oriented to bend the workpiece. The drive roll continues its clockwise rotation to complete the bending of workpiece 136.

In this version of the machine, all three of the rolls are tapered, to minimize or avoid slippage of the workpiece between drive roll 130 and the roll that is functioning as the pinch roll. As to the bending function, each of rolls 132 and 134 is movable independently at its opposite ends to adjust the roll orientation or angle, taking into account the taper of the roll.

Another feature of the machine, and of machine 16 as well, is that the drive roll and the pinch roll do not need to be the same size. So long as the drive roll and the pinch roll exhibit the same ratio of small-end to large-end radii, and each roll is tapered in uniform fashion from one end to the other, the larger roll can be rotated at a lower rate as compared to the smaller roll, yet exhibit the same linear or tangential velocity as the smaller roll at any given location along the confronting surfaces of the rolls. Further in this case, the larger and smaller rolls exhibit the same rate of increase in tangential velocity in the direction of roll divergence. The result, as before, is to eliminate workpiece skidding or slippage.

FIGS. 13 and 14 schematically illustrate the three rolls of a further alternative embodiment machine of the “single/initial pinch” type. A drive roll 138 is powered to rotate relative to a machine frame (not shown) about a drive-roll axis fixed with respect to the frame. A pinch roll 140 is rotatable relative the frame about a pinch roll axis. In a manner similar to machine 16, rolls 138 and 140 are tapered and oriented with their respective rotational axes slightly inclined relative to a longitudinal direction (perpendicular to the plane of FIGS. 13 and 14) so that their confronting surfaces are parallel. Pinch roll 140 further is movable toward and away from drive roll 138 along a transverse path, with its orientation maintained to preserve parallelism of the opposing surfaces.

A forming roll 142 is rotatable about a forming-roll axis, and further is movable relative to the frame along an arcuate or linear path, generally transversely relative to the frame. Opposite ends of forming roll 142 are movable independently as before, to allow selective orientation of the roll.

A flat workpiece 144 is shaped by initially positioning its leading edge 146 between rolls 138 and 140. Forming roll 142 is advanced against the workpiece, and properly oriented (angled) to achieve the desired bending of the workpiece, both initially and as rolls 138 and 140 are counter-rotated to move the workpiece through the machine.

At some point before a trailing edge 148 of workpiece 144 reaches forming roll 142, the counter-rotation is stopped and pinch roll 140 is withdrawn to release the workpiece. The workpiece is reloaded, this time with edge 148 between rolls 138 and 140. As seen in FIG. 14, workpiece 144 is curved as it extends away from rolls 138 and 140 in the opposite direction as compared to the initial loading in FIG. 13. This is occasioned by the need to match the longer side edge of the workpiece with the larger-diameter location along the drive and pinch rolls. With reference to FIG. 14, forming roll 142, having previously been moved to a clearance position shown in broken lines at 142 a, is advanced against workpiece 144 to the position shown in solid lines and again properly oriented. At this stage, rolls 138 and 140 are counter-rotated to move the workpiece through the machine to complete the desired curvature.

Compared to this approach, machine 16 is more costly from the standpoint of requiring an additional forming roll. However, the additional roll advantageously eliminates the need to remove and reload each workpiece.

Thus in accordance with the present invention, flat workpieces such as generally trapezoidal panels are consistently and accurately shaped into truncated cones and truncated conical sections for assembly into containers with frusto-conical walls and wall sections. Panels of a given width can be shaped according to a desired ratio of small-end radius to large-end radius, inclined to provide the desired ratio. In addition, drive and pinch rolls longer than required, in combination with guides for selectively positioning workpieces along the rolls, enable a selective adjustment of radii ratios over a desired range, to facilitate fabrication of differently inclined conical wall sections. 

1. A roll forming machine, including: an elongate first roll having a first roll axis and substantially uniformly tapered over a first region extending axially between a first axial location having a first diameter and a second axial location having a second diameter larger than the first diameter; an elongate second roll having a second roll axis and substantially uniformly tapered over a second region extending axially between a third axial location having a third diameter and a fourth axial location having a fourth diameter larger than the third diameter; an elongate third roll rotatable on a third roll axis; and a roll mounting structure coupled to the first and second rolls to support the first and second rolls in side-by-side relation for rotation about the first and second roll axes, respectively; with the first axial location proximate the third axial location and the second axial location proximate the fourth location; and with the first and second rolls inclined relative to one another whereby the first and second roll axes intersect and first and second confronting surfaces of the first and second regions extend longitudinally, separated by a substantially constant transverse spacing to facilitate a frictional hold of a uniformly thick workpiece between the first and second regions with a major plane of the workpiece perpendicular to an alignment plane containing the first and second roll axes; wherein the roll mounting structure is operable to counter-rotate the first and second rolls about the first and second axes respectively during said frictional hold, thereby to effect a rotation of the workpiece about a transverse rotational axis lying in the alignment plane; and wherein the roll mounting structure further is coupled to support the third roll in side-by-side, transversely spaced apart relation to the first and second rolls, and is operable to selectively move the third roll transversely relative to the first and second rolls to apply a predetermined bending force to the workpiece during said hold and rotation.
 2. The machine of claim 1 wherein: the second roll is movable transversely relative to the first roll to selectively adjust the transverse spacing.
 3. The machine of claim 2 further including: a workpiece alignment component adapted to facilitate locating a leading edge region of a workpiece between the first and second rolls in a predetermined initial position for said hold.
 4. The machine of claim 3 wherein: the workpiece alignment component comprises a stop positioned to abut the leading edge region as the workpiece is inserted transversely between the first and second rolls, to prevent further transverse movement of the workpiece beyond the predetermined initial position.
 5. The machine of claim 4 wherein: the workpiece alignment component further includes a guide member positioned to contact a side edge of a workpiece as the workpiece is inserted between the first and second rolls, to determine a longitudinal location of the workpiece with respect to the first and second rolls.
 6. The machine of claim 5 wherein: the stop and the guide member are retractable away from the first and second rolls after movement of the second roll transversely toward the first roll to effect said hold.
 7. The machine of claim 3 wherein: the workpiece alignment component comprises a first side edge contact feature positioned to contact a side edge of a workpiece as the workpiece is inserted between the first and second rolls to determine a first longitudinal location of the workpiece with respect to the first and second rolls, and a second side edge contact feature spaced apart longitudinally from the first contact feature and positioned to contact the side edge of the workpiece as the workpiece is inserted between the first and second rolls, to determine a second longitudinal location of the workpiece with respect to the first and second rolls.
 8. The machine of claim 1 further including: a fourth roll rotatable on a fourth roll axis, wherein the roll mounting structure further is coupled to the fourth roll to support the fourth roll in side-by-side, transversely spaced apart relation to the first and second rolls on an opposite side of said alignment plane from the third roll; wherein the roll mounting structure further is operable to selectively move the fourth roll transversely relative to the first and second rolls to apply the predetermined bending force to the workpiece during said hold and rotation.
 9. The machine of claim 1 wherein: the third roll has a substantially uniform diameter over its entire length.
 10. The machine of claim 1 further including: a first motive power source operatively coupled to the first roll for rotating the first roll about the first roll axis.
 11. The machine of claim 1 wherein: the confronting surfaces of the first and second rolls are inclined from the first and second roll axes respectively at an angle within the range of one to five degrees.
 12. The machine of claim 1 wherein: the first and third diameters are substantially equal, and the second and fourth diameters are substantially equal.
 13. An apparatus for shaping substantially planar sheet metal panels into truncated conical wall sections for a drum, including: a first elongate truncated conical roll having a first roll axis; a second elongate truncated conical roll having a second roll axis; a roll mounting structure coupled to the first and second rolls to support the first and second rolls in side-to-side relation, tapered in the same direction, and inclined such that the first and second roll axes intersect and confronting first and second surface portions of the first and second rolls, respectively, extend longitudinally and are separated from one another by a substantially uniform transverse spacing; a power component operatively coupled to the first roll for counter-rotating the first and second rolls about the first and second roll axes respectively with a substantially planar formable sheet metal panel frictionally held by a thickness thereof between the first and second confronting surface portions, to rotate the panel about a transverse rotational axis lying in an alignment plane defined by the first and second roll axes; and a panel bending component operable to apply a controlled bending force to the panel substantially in the direction of said thickness while the panel is so held and so rotated.
 14. The apparatus of claim 13 wherein: the panel bending component comprises an elongate third roll rotatable on a third axis, wherein the roll mounting structure supports the third roll in side-by-side transversely spaced apart relation to the first and second rolls with the third roll axis directed substantially longitudinally, and is operable to selectively move the third roll transversely relative to the first and second rolls to apply the bending force.
 15. The machine of claim 14 wherein: the panel bending component further comprises a fourth roll rotatable on a fourth roll axis; the roll mounting structure further supports the fourth roll in side-by-side, transversely spaced apart relation to the first and second rolls with the forth axis directed substantially longitudinally and on an opposite side of said alignment plane from the third roll; and the roll mounting structure further is operable to selectively move the fourth roll transversely relative to the first and second rolls to apply the bending force.
 16. The apparatus of claim 13 wherein: the second roll is moveable transversely relative to the first roll to selectively adjust the transverse spacing.
 17. The apparatus of claim 16 wherein: the power component further is operatively coupled to the second roll to simultaneously rotate the first and second rolls in opposite angular directions.
 18. The apparatus of claim 16 further including: an alignment component adapted to facilitate locating a leading edge region of a panel between the first and second rolls in a predetermined initial position for said hold.
 19. The apparatus of claim 18 wherein: the alignment component comprises a stop positioned to abut the leading edge region as the panel is inserted transversely between the first and second rolls, to prevent further transverse movement of the panel beyond the predetermined initial position.
 20. The apparatus of claim 19 wherein: the alignment component further includes a guide member positioned to contact a side edge of a panel as the panel is inserted between the first and second rolls, to determine a longitudinal location of the panel with respect to the first and second rolls.
 21. The apparatus of claim 20 wherein: the stop and the guide member are retractable away from the first and second rolls following movement of the second roll transversely toward the first roll.
 22. The apparatus of claim 18 wherein: the alignment component comprises a first guide member positioned to contact a side edge of a panel as the panel is inserted between the first and second rolls to determine a first longitudinal location of the panel with respect to the first and second rolls, and a second guide member spaced apart longitudinally from the first guide member and positioned to contact the side edge of a panel as the panel is inserted between the first and second rolls, to determine a second longitudinal location of the panel with respect to the first and second rolls.
 23. A process for forming planar malleable panels according to conical geometries, including: a. providing a conical drive roll and a conical pinch roll rotatable about respective drive roll and pinch roll axes and inclined relative to each other whereby said axes intersect to define an alignment plane, with first and second confronting surfaces of the drive and pinch rolls, respectively, extending longitudinally and separated from one another by a substantially uniform transverse spacing; b. providing a substantially planar and uniformly thick panel formed of a malleable material with oppositely inclined leading and trailing edges, substantially parallel side edges, and a leading edge region adjacent to and incorporating the leading edge; c. positioning the panel with the leading edge region disposed between the first and second confronting surfaces, with a major plane of the panel perpendicular to the alignment plane, and with the leading edge extending longitudinally; d. with the panel so positioned, transversely moving at least one of the drive roll and the pinch roll to reduce the transverse spacing to effect a frictional hold of the panel between the drive roll and the pinch roll; e. during the frictional hold, counter-rotating the drive roll and the pinch roll to rotate the panel about a transverse rotational axis perpendicular to the alignment plane; and f. while so rotating the panel, applying a controlled bending force to the panel in a direction substantially perpendicular to the major plane.
 24. The process of claim 23 wherein: positioning the panel comprises placing the leading edge of the panel against a stop positioned between the drive roll and the pinch roll.
 25. The process of claim 23 wherein: positioning the panel comprises disposing one of the side edges of the panel against a first guide member disposed proximate the drive roll and the pinch roll.
 26. The process of claim 23 wherein: positioning the panel comprises disposing one of the panel side edges against a selected one of a plurality of longitudinally spaced apart guide members disposed proximate the drive roll and the pinch roll, thereby to select one of several alternative longitudinal locations of the panel with respect to the drive roll and the pinch roll.
 27. The process of claim 23 wherein: transversely moving at least one of the drive roll and pinch roll comprises moving the pinch roll toward the drive roll.
 28. The process of claim 23wherein: counter-rotating the drive roll and the pinch roll comprises coupling a source of motive power to rotate the drive roll about the drive roll axis, while rotating the pinch roll about the pinch roll axis by virtue of its frictional coupling to the drive roll through the panel.
 29. The process of claim 23 wherein: counter-rotating the drive roll and the pinch roll comprises coupling a first source of motive power to rotate the drive roll about the drive roll axis and coupling a second source of motive power to rotate the pinch roll about the pinch roll axis, to rotate said rolls in opposite angular directions and at the same angular speed.
 30. The process of claim 23 wherein: applying a controlled bending force comprises supporting an elongate first bending roll for rotation about a substantially longitudinal first bending roll axis in transversely spaced apart relation to the drive roll and the pinch roll on a first side of the alignment plane, and moving the first bending roll transversely against the panel to apply the bending force.
 31. The process of claim 30 wherein: applying the bending force further comprises supporting a second bending roll with a substantially longitudinal second bending roll axis in transversely spaced apart relation to the drive roll and the pinch roll on a second and opposite side of the alignment plane, and moving the second bending roll transversely against the panel to apply the bending force.
 32. The process of claim 23 further including: repeating steps b. through f. several times to form a plurality of frusto-conically shaped panels, each with arcuate first and second opposite edges having respective first and second different radii and encompassing an arc of less than 360 degrees; assembling the panels end to end with the leading and trailing edges of adjacent panels contiguous, to from a continuous frusto-conical wall section encompassing 360 degrees; and with the panels so assembled, bonding the contiguous leading and trailing edges to form an integral frusto-conical wall section. 